• Geomechanics and Engineering
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• 제29권6호
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• pp.645-655
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• 2022

Granular columns have recently found widespread use in underground construction. The behaviour of granular columns under vertical loads has been extensively studied, specifically in relation to vertical load capacity obtained by bulging of the column body, including the behaviour after encasement of material. Determining the shear strength of loose soils reinforced with granular columns has received less attention. After the observations of lateral deformation near the toe of the embankment, attempts have been made to strengthen the lateral strength of granular columns. The purpose of this research is to look into the effects of different encasement conditions on the lateral load capacity of granular columns. This was accomplished by three-dimensional finite element analysis with FEM software. Various normal pressures and two different encasement configurations, namely single layer encasement and double layer encasement, with differing tensile strengths, were used in this study to determine their effect on lateral resistance. The failure envelope for a single column planted in loose sand was used to analyse the findings for three different granular column diameters, as well as the impact of different encasement conditions. According to the findings, the inclusion of a Granular Column enhanced the shear strength and overall stiffness of the loose sand bed, and the encasement of the Granular Column helped in deriving higher lateral resistance.

• Geomechanics and Engineering
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• 제12권3호
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• pp.417-439
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• 2017

The stone columns are increasingly being used as a soil improvement method for supporting a wide variety of structures (such as road embankment, buildings, storage tanks etc.) especially built on soft soil. Soil improvement by the stone column method overcomes the settlement problem and low stability. Nevertheless, stone column in very soft soils may not be functional due to insufficient lateral confinement. The required lateral confinement can be overcome by encasing the stone column with a suitable geosynthetic. Encasement of stone columns with geogrid is one of the ideal forms of improving the performance of stone columns. This paper presents the results of a series of experimental tests and numerical analysis to investigate the behavior of stone columns with and without geogrid encasement in soft clay deposits. A total of six small scale laboratory tests were carried out using circular footing with diameters of 0.05 m and 0.1 m. In addition, a well-known available software program called PLAXIS was used to numerical analysis, which was validated by the experimental tests. After good validation, detailed of parametric studies were performed. Different parameters such as bearing capacity of stone columns with and without geogrid encasement, stiffness of geogrid encasement, depth of encasement from ground level, diameter of stone columns, internal friction angle of crushed stone and lateral bulging of stone columns were analyzed. As a result of this study, stone column method can be used in the improvement of soft ground and clear development in the bearing capacity of the stone column occurs due to geogrid encasement. Moreover, the bearing capacity is effected from the diameter of the stone column, the angle of internal friction, rigidity of the encasement, and depth of encasement. Lateral bulging is minimized by geogrid encasement and effected from geogrid rigidity, depth of encasement and diameter of the stone column.

• Geomechanics and Engineering
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• 제32권6호
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• pp.567-581
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• 2023

Enhanced vertical load capacity of the ground reinforced with the stone columns drew great attention by the researchers as it deals with many of the geotechnical difficulties associated with the weak ground. Recently, it has been found that the stone columns are also prone to fail under the shear load when employed beneath the embankments or the foundations susceptible to lateral loads. In this study, the effect of various encasement conditions on the lateral deflection of stone columns is investigated. A method of dual layers of encasement has been introduced and its the effect on lateral load capacity of the stone columns has been compared with those of the single encased stone column and the un-encased stone columns. Large shear box tests were utilised to generate the shear deformation on the soil system under various normal pressure conditions. The stiffness of the soil-stone column combined system has been compared for various cases of encasement conditions with different diameters. When subjected to lateral deformation, the encased columns outperformed the un-encased stone columns installed in loose sand. Shear stress resistance is up to 1.7 times greater in dual-layered, encased columns than in unencased columns. Similarly, the secant modulus increases as the condition changes from an unencased stone column to single-layer encasement and then to dual-layer encasement, indicating an improvement in the overall soil-stone column system.

• 한국지반공학회논문집
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• 제27권2호
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• pp.73-80
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• 2011

본 논문에서는 지오그리드 감쌈쇄석말뚝 공법의 현장적용을 위한 지오그리드 감쌈 제작방법 에 관한 실험적 내용을 다루었다. 지오그리드 감쌈 제작방법에 따른 지오그리드 쇄석기둥의 지지력 증가 특성과 변형특성 평가를 위해 중대형 압축시험을 수행하였다. 실험결과를 통해 지오그리드 감쌈 제작시 지오그리드 겹침 제작은 효율적인 방법임을 알 수 있으며,쇄석기둥 상부영역에서 지오그리드 감쌈 제작방법에 따른 접합부위의 품질관리 방안이 중요함을 알 수 있다. 실험결과를 통해 현장적용시 GESC의 충분한 보강효과를 발휘하기 위한 지오그리드 감쌈 제작 방안을 제시하였다.

• Structural Engineering and Mechanics
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• 제65권1호
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• pp.81-89
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• 2018

Stone column installation is a convenient method for improvement of soft ground. In very soft clays, in order to increase the lateral confinement of the stone columns, encasing the columns with high stiffness and creep resistant geosynthetics has proved to be a successful solution. This paper presents the results of three dimensional finite element analyses for evaluating improvement in behaviour of ordinary stone columns (OSCs) installed in soft clay by geotextile encasement under monotonic and cyclic loading by a comprehensive parametric study. The parameters include length and stiffness of encasement, types of stone columns (floating and end bearing), frictional angle and elastic modulus of stone column's material and diameter of stone columns. The results indicate that increasing the stiffness of encasement clearly enhances cyclic behaviour of geotextile encased stone columns (GESCs) in terms of reduction in residual settlement. Performance of GESCs is less sensitive to internal friction angle and elasticity modulus of column's materials in comparison with OSCs. Also, encasing at the top portion of stone column up to triple the diameter of column is found to be adequate in improving its residual settlement and at all loading cycles, end bearing columns provide much higher resistance than floating columns.

• Geomechanics and Engineering
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• 제19권4호
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• pp.329-342
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• 2019

In this paper, the effect of a group of sand columns in the loose soil bed using triaxial tests was studied. To investigate the effect of geotextile reinforcement type on the bearing capacity of these sand columns, Vertical encased sand columns (VESCs) and horizontally reinforced sand columns (HRSCs) were used. Number of sixteen independent triaxial tests and finite element simulation were performed on specimens with a diameter of 100 mm and a height of 200 mm. Specimens were reinforced by either a single sand column or three sand columns with the same area replacement ratio (16%) to evaluate the Influence of the column arrangement. Effect the number of sand columns, the length of vertical encasement and the number of horizontal reinforcing layers were investigated, in terms of bearing capacity improvement and economy. The results indicated that the ultimate bearing capacity of the samples with three ordinary sand columns (OSCs) is eventually about 11% more than samples with an OSC. Also, comparison of the column reinforcing modes showed that four horizontal layers of geotextile achieved similar performance to a vertical encasement geotextile at the 50% of the column height, from the viewpoint of strength improvement, while from the viewpoint of economy, the geotextile needed for encasing the single column is around 2.5 times of the geotextile required for four layers.

• 한국강구조학회 논문집
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• 제27권6호
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• pp.525-536
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• 2015

콘크리트피복 충전강관의 휨-압축 성능을 평가하기 위한 편심압축실험을 수행하였다. 기둥 주철근의 국부좌굴을 구속하고 콘크리트피복의 조기파괴를 방지하기 위하여 U형 띠철근 상세를 제안하였다. 주요 실험변수는 축하중 편심거리, 띠철근 간격, 그리고 콘크리트피복 여부이다. 실험결과 얇은 콘크리트피복에 수직균열이 조기에 발생하였지만 실험체의 최대강도는 콘크리트 피복의 기여도를 고려한 예측강도를 만족하였다. 또한, 내부 원형강관으로 인하여 제안된 콘크리트피복 충전강관은 우수한 변형능력을 나타냈다. 실험체의 휨-압축 강도 및 휨강성을 현행 설계기준과 비교하여 분석하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.396-404
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• 2009

This paper presents the results of numerical investigation on support mechanism of geogrid-encased stone columns for use in soft ground. A number of cases were analyzed using a axial- and 3D stress-pore pressure coupled model that can effectively model construction sequence and drainage as well as reinforcing effects of geogrid-encased stone columns. The results indicated that the geogrid encasement tends to significantly improve the load carrying of a stone column. Also revealed was that such a confinement effect depends on encasement length and stiffness of geogrid. It is also shown that there exist critical encasement length and stiffness of geogrid for a given condition.

• 한국지반신소재학회논문집
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• 제7권4호
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• pp.25-36
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• 2008

본 논문에서는 수치해석적 접근을 통해 연약지반에 시공되는 지오그리드 감쌈 스톤컬럼의 하중지지 특성을 고찰한 내용을 다루었다. 지오그리드로 감싼 스톤컬럼의 보강효과에 대해 검증된 유한요소모델을 이용하여 축대칭 및 3차원 응력-간극수압연계해석을 토대로 매개변수 연구를 수행하였다. 해석결과를 종합한 결과 지오그리드로 감싼 스톤컬럼의 하중지지 특성이 향상되는 경향을 나타내었다. 아울러 보강재의 감쌈길이와 축강성이 지오그리드 감쌈 스톤컬럼의 주된 설계변수가 되며, 지오그리드 보강효과를 극대화 할 수 있는 지오그리드의 임계감쌈길이 및 임계강성이 존재하는 것으로 나타났다.

• 한국지반공학회논문집
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• 제23권5호
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• pp.15-27
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• 2007

본 논문에서는 사질토 지반에 시공되는 고강도 지오그리드 보강 쇄석말뚝(Geosynthetic-Reinforced Stone Column, GRSC)의 다양한 영향인자 검토를 통한 지지력 거동특성을 다루었다. 본 연구는 GRSC의 국내 적용을 위한 사전연구로서 대형 구조물의 기초지지 말뚝으로 적용시를 대상으로 2차원 유한요소 해석을 수행하였다. 유한요소해석 결과 GRSC와 쇄석말뚝(Stone Column, SC)의 비교를 통해 지오그리드 보강이 지지력 증가에 현저히 영향을 미치는 것으로 나타났다. 또한 지반강도와 쇄석기둥 직경, 지오그리드 강성에 대해 지지력은 증가하는 것으로 나타난 반면, 감쌈길이에 대해서는 3D(D=쇄석기둥 직경)이상의 감쌈에 대해 지지력이 수렴하는 것으로 분석되었다. 따라서 본 연구에서는 GRSC 적용시 효율적인 지오그리드 보강의 최적조건을 제안하였다.